1. Field Of The Invention
The present invention relates to fiber-reinforced poly(biphenylene sulfide) composites having improved mechanical properties and methods of producing such composites.
2. Description of the Prior Art.
Reinforced poly(arylene sulfide) composites are highly suitable for forming a variety of parts and objects. Because of their outstanding chemical, heat and electrical insulation resistance as well as their superior rigidity when compared to other thermoplastics, poly(arylene sulfide) resins have found favor for forming reinforced plastic composites.
A particularly suitable poly(arylene sulfide) resin for forming fiber-reinforced composites, both by injection molding and pultrusion techniques, has been found to be poly(phenylene sulfide) resin. Fiber-reinforced poly(phenylene sulfide) composites exhibit excellent mechanical properties and are utilized in a great variety of products. However, in product applications where very high temperature exposure is required, e.g., temperatures in the range of from about 400.degree. F. to about 600.degree. F., poly(phenylene sulfide) composites generally do not maintain high rigidity and strength.
A poly(arylene sulfide) resin which has heretofore been found to have a very high melting point and to be suitable for use at very high temperatures is poly(biphenylene sulfide) resin. Poly(biphenylene sulfide) resin retains its hardness at temperatures as high as about 700.degree. F. whereas poly(phenylene sulfide) resin loses hardness at temperatures in the range of from 300.degree. F. to 400.degree. F. Composites comprised of reinforcing fibers in a continuous matrix of poly(biphenylene sulfide) resin, in addition to having high melting points, also generally have high retention of mechanical properties at elevated temperatures. For example, such composites generally maintain full rigidity and strength (compared to their rigidity and strength at room temperature) up to about 400.degree. F. At 600.degree. F. the composites generally retain about 80% and 35% of their room temperature flexural modulus and flexural strength, respectively.
Heretofore, poly(biphenylene sulfide) resin has been prepared from sodium sulfide and either 4,4'-dichlorobiphenyl or 4,4'-dibromobiphenyl. The resin prepared from 4,4'-dichlorobiphenyl is superior to that which is prepared from 4,4'-dibromobiphenyl. However, the use of polychlorinated biphenyl has been discontinued as a result of its having been found to be hazardous to human health.
By the present invention improved composites comprised of reinforcing fibers in a continuous matrix of poly(biphenylene sulfide) resin and methods of preparing such composites are provided. The resin utilized in accordance with the present invention has a higher melting point and a higher melt viscosity as compared to poly(biphenylene sulfide) resin formed from sodium sulfide and 4,4'-dibromobiphenyl. As a result, the composites of the invention have better mechanical properties at room temperature and better retention of mechanical properties at elevated temperatures.